Fix indent error

When all cells are mute, get_availability_zones crashes with
a None type is not iterable error.

Change-Id: I2ede1326aaa5fe5cea96b216a3fa7fc4105b7d69
Fix typo in AZ cache key

Change-Id: Ifc8d300abf453e1ed315550c0f46b7b2697eb4de